Non-sticking electrical contacts



g- 25, 1964 w. P. MASON ETAL 3,146,328

NON-STICKING ELECTRICAL CONTACTS Filed Nov. 7, 1961 2 Sheets-Sheet 1SOURCE POTENTIAL FIG. 2

.wP. MASON WVENTORSM E. S/KORSK/ 524 & MW

1964 w. P. MASON ETAL NON-STICKING ELECTRICAL CONTACTS 2 Sheets-Sheet 2Filed Nov. 7, 1961 FIG. 3 PRIOR ART FIG. 4' PRIOR ART m P MASON MENTORM. E. S/KORSK/ ATTORNEY 3,146,328 Patented Aug. 25, 1964 ice I 3,146,328NON-STICKING ELECTRICAL CONTACTS Warren P. Mason, West Orange, andMathew E. Sikorski,

New Providence, N.J., assignors to Bell Telephone Laboratories,Incorporated, New York, N.Y., a corporation of New York Filed Nov. 7,1961, Ser. No. 150,810 1 Claim. (Cl. 200-165) This invention relates toelectrical contacts and more particularly to electrical contacts whichwill not tend to adhere or stick to each other.

Difiiculties resulting from the adhesion or sticking of electricalcontacts employed in making and breaking electrical circuit connectionsare frequently encountered with many prior art devices. Thesedifiiculties include not only the electrical malfunctioning of theconnecting mechanisms but also the rapid mechanical deterioration of thecontacting surfaces by abrasion, pitting and the like. In many instancesadhesion between the contacting surfaces has resulted in the virtualwelding together of appreciable portions of the two contacting surfaces.Subsequent separation of the members then frequently results in tearingpieces out of one or both surfaces.

In accordance with the present invention, such difficulties aresubstantially reduced by employing specific conductive materials for oneor both of the contacting surfaces which have been found to haverelatively very low coetficients of adhesion.

Accordingly, the present invention proposes the use of a metal selectedfrom the group consisting of cadmimum, cobalt, beryllium, titanium andzirconium. Metals of this group have low coefiicients of adhesion andgenerally acceptable electrical characteristics. Preferably, for contactpairs one contacting surface is one of the above group of metals and theother is of a noble metal. Metals of the group consisting of gold,silver, ruthenium, rhodium, palladium, osmium, iridium and platinum aredesignated as noble metals by those skilled in the art. A number ofthese, particularly gold, silver, palladium and platinum, have beenextensively used as electrical contacts since they have low electricalresistance and tend to be self-cleaning. In general, where a pair ofcontacts is to comprise one metal of the first group above-mentioned andone of the group designated noble, they are preferably selected to be ofapproximately comparable hardness. For example, for a pair employing onecontact of cobalt the noble metal contact can preferably be rhodium.This specific combination has been found to be very satisfactory, givingnegligible sticking difliculty and low electrical resistance. As is wellknown in the art, noble metal contacts are in practice frequently alloyshaving appreciable percentages (for example, ten to fifteen percent) ofbase metals to increase their wear-resisting properties or otherwiseimprove their characteristics For the purposes of the present invention,the noble metals specified may be of pure metal or of the conventionalalloy forms normally employed for electrical contacts.

For switches employing mercury-wetted contacts, the present inventionparticularly recommends the further metal rhenium, since it does notform an amalgam with mercury. The sticking of mercury-wetted contactshas in many instances been found to have resulted from the formation ofamalgams on the contacts. A second combination which has been found tohave low electrical resistance and to be substantially free fromsticking in devices employing mercury-wetted contacts is the paircomprising one contact of the noble metal ruthenium and the othercontact of a platinum nickel alloy. The addition of a minor percentage(such as ten or twelve percent) of nickel in an alloy with platinumincreases the facility with which it can be wetted with liquid mercury.

In general, cadmium, cobalt and rhenium are readily plated on themajority of other metals. Beryllium, titanium and zirconium mustordinarily be welded on other metals. Substantially all of the noblemetals are readily plated on most other metals.

In the accompanying drawings, several differing types of electricalswitching arrangements are illustrated and exemplify the application ofthe invention to such arrangements.

In FIG. 1, one form of a dry reed type of switching mechanism is shown;

In FIG. 2, one form of a switching mechanism employing mercury-wettedcontacts is shown;

In FIG. 3, one form of a printed circuit assemblage is shown; and

In FIGS. 4 and 5 details of the assemblage of FIG. 3 of particularinterest in connection with the application of the principles of thepresent invention are shown.

In more detail, in FIG. 1 a switching mechanism of a general typedisclosed and claimed in applicant W. P. Masons copending applicationSerial No. 847,235 filed October 19, 1959, which matured as Patent No.3,008, 020, granted November 7, 1961 is shown to an enlarged scale.Insofar as it is pertinent, this copending application is incorporatedby reference as an integral portion of the disclosure of the presentapplication.

As described in the aforementioned copending sole application, thearrangement of FIG. 1 includes a reedtype, magnetically-operable,switching mechanism comprising a sealed glass envelope 16, five-eighthsof an inch long and one-eighth of an inch in diameter, into which aresealed reeds 12 and 14 supported by being embedded in the right and leftend seals, respectively, of envelope 16, as shown, so that their freeends are held in close proximity though not in physical contact.

Reeds 12 and 14- are of magnetic material so that when subjected to asuitably directed magnetic field they will be drawn together to makephysical and electrical contact and thus close a circuit which includesutilization circuit 10, as shown. Reeds 12 and 14 are sufiicientlyresilient that they will return to their original positions when themagnetic field, including the remanent magnetic field, is appropriatelyreduced, as above described, thus opening the circuit includingutilization circuit 10.

The toroidal C-shaped yoke 20, with its gap uppermost, is recessedtransversely with respect to the gap at the top so that the cylindricaltube 16 can be assembled in the transverse recess with the free ends ofreeds 12, 14 in the gap of yoke 20 as shown. Yoke 20 is of a bistablemagnetic material such as a ferrite in which remanent polarization isreadily established by passing a very short pulse of direct currentthrough conductor 22, which conductor passes through the central openingin yoke 20. The polarity of the polarization will of course be reversedif the direction of the pulse in conductor 22 is reversed. The materialof yoke 20 is chosen so that a suitable degree of remanent polarizationto hold the reeds 12 and 14 in contact will be established by anextremely short pulse of the appropriate polarity. The contacts may,accordingly, be operated by a pulse hav ing a duration of onemicrosecond or less.

A source of potential 24 controlled through single pole, double throwswitch 26 can furnish momentary directcurrent pulses of either polarityand of appropriate magnitude to conductor 22.

As shown in FIG. 1, a portion of the glass tube 16 and a portion of theyoke 24) are broken away to expose the adjacent ends of reeds 12 and 14so that the character of the structure can be more readily perceived. Itis to be understood however that in use a complete yoke and completetube are employed.

A small permanent magnet 18 is employed immediately above the gap inyoke 20, as shown, and is polarized in such a direction that it tends toaid a direct-current pulse of appropriate polarity in establishingsuflicient remanent polarization of yoke as required to hold reeds 12and 14 in contact, that is, in the closed position. The strength ofmagnet 18 is however insufiicient to establish an operated or closedcondition of the switch unless aided by the pulse. A similardirect-current pulse, but of opposite polarity, will sufficiently reducethe remanent polarization of yoke 20 so that the resilience of reeds 12,14 will cause them to separate.

In accordance with the present invention the surfaces at the free endsof reeds 12 and 14 which establish electrical contact are covered, forexample, the upper one with a contacting surface 30 of a metal selectedfrom the group consisting of cadmium, cobalt, beryllium, titanium andzirconium and the lower with a contacting surface 32 of a noble metalfrom the group consisting of gold, silver, ruthenium, rhodium,palladium, osmium, iridium and platinum.

Since metals of the first group have very low coefficients of adhesionand metals of the second group have excellent conductive andself-cleaning properties, switches employing the above prescribedcontact pairs will not weld together, stick nor tend to prematurelywear, pit, or otherwise deteriorate. Alternatively, both end surfaces ofreeds 12 and 14 can be covered by a metal of the first group Whereminimum contact resistance and self-cleaning properties are not ofprimary importance.

In FIG. 2 an improved switching mechanism of a type which employsmercury-wetted contacts is shown to an enlarged scale. With theexception of the right and left pairs of contacts 44 and 46, assembly 40of FIG. 2 can be precisely as described in Patent 2,868,926 grantedJanuary 13, 1959, to C. E. Pollard, assignor to applicants assignee. Thedescription of Patent 2,868,926 pertinent to assembly 40 is herebyincorporated by reference and made an integral portion of the presentapplication.

As described in the Pollard patent, a glass envelope 41 encloses theswitching mechanism and serves to support, by an arrangement describedin detail in the patent, the armature 42, intermediate the fixedconductive members 48 in the respective positions shown so thatdirect-current energy applied to winding 43 will deflect armature 42 tothe right for one polarity or to the left for the opposite polarity,respectively, thus closing the right or left pairs of contacts 44, 46,respectively. As described in the Pollard patent, sufficient mercury isdrawn upwardly along armature 42 by capillary action so that bothcontacts 44 are maintained with a complete covering of liquid mercury,that is, they are mercury-wetted. Contacts 46 become mercury-wetted bycontact with their respective associated contacts 44 in normal operationof the switch.

In accordance with the teachings of the present invention, for each pairof contacts 44, 46 one of the contacts should be of a metal selectedfrom the group consisting of rhenium, cadmium, cobalt, beryllium,titanium and zirconium and the other should be of a noble metal asdefined hereinabove. Of the first-mentioned group of metals, rhenium ispreferable Where, as in the present instance, mercury-wetted contactsare employed, since, as mentioned above, rhenium does not form anamalgam with mercury and has a low coefficient of adhesion.Alternatively, both contacts may be of a metal selected from thefirst-mentioned group and again the metal rhenium is preferable for thereason stated above. A further very satisfactory, non-sticking, lowelectrical resistance contact combination when mercury-wetted contactsare used has been found, as mentioned above, to comprise one contact ofruthenium paired with a contact of a platinum nickel alloy.

In FIG. 3, an over-all assembly of the type disclosed and claimed inUnited States Patent 2,832,013 granted April 22, 1958, to L. Pedersenand A. J. Wier, assignors to applicants assignee, is shown. This isdesignated in the joint patent as a printed wire circuit cardinterconnection apparatus. The designation is obviously succinctlydescriptive of the assembly. A detailed description is, of course, givenin the patent.

In FIG. 4 a partial cross-sectional showing of the connections of arepresentative card of the assembly of FIG. 3 to the wires of the frameis shown to a somewhat larger scale. In FIG. 5 the details of anindividual connecting clip are shown to a still larger scale.

Except for the provision of special contacting surfaces 56 and 58 forthe connecting clip prongs 52 and 54, respectively, as shown in. FIG. 5of the present application, which will be described in more detailhereinunder, the apparatus may be precisely as described in theabovementioned joint patent. FIGS. 3, 4 and 5 of the drawings of thepresent application are, with the above noted exception, substantiallyidentical with FIGS. 1, 3 and 4, respectively, of the joint patent. Thedisclosure of the joint patent pertinent to the present application isaccordingly incorporated by reference and made an integral part of thedisclosure of the present application.

In FIG. 5, the connecting clip 50 may be precisely identical with thatshown in FIG. 4 of the above-mentioned joint patent to Pedersen and Wierexcept that the bifurcated contacting fingers 52 and 54 of the clip 50are equipped on their inner surfaces with metal layers 56 and 58, asshown, which serve to make mechanical and electrical contact with anassociated predetermined interconnecting wire 60 of the rack asesmbly 70of FIG. 3 for the purposes set forth in detail in the above-mentionedjoint patent.

In accordance with the present invention, metal layers 56 and 58 are ofa metal selected from the group which consists of cadmium, cobalt,beryllium, titanium and zirconium. Wire 60 may be coated with a metalfrom this group or alternatively and preferably, it may be coated with anoble metal selected from the group consisting of gold, silver,ruthenium, rhodium, palladium, osmium, iridium and platinum. Numerousother forms of assemblies employing plug-in apparatus units are wellknown in the art and can obviously employ the teachings of the presentinvention to advantage.

Numerous and varied other switching arrangements will readily occur tothose skilled in the art fully within the spirit and scope of thepresent invention. No attempt to cover all such arrangements has beenmade, the above disclosed arrangements being fairly illustrative butobviously not restrictive with respect to the application of theprinciples of the invention.

What is claimed is:

Switching means in which an electrical circuit is opened and closed byseparating and bringing together, respectively, two metallic members,one of said members being of cobalt and the other of rhodium.

References Cited in the file of this patent UNITED STATES PATENTS2,253,672 Wolter Aug. 26, 1941 2,733,319 Ericsson et al Jan. 31, 19562,769,875 Brown et al. Nov. 6, 1956 2,901,580 Kelly Aug. 25, 1959

